Trolley diverter

ABSTRACT

The system has over and under propelling member and trolley tracks of constant spacing. The propelling member has a depending driving arm for engaging the trolleys and a normally retracted pivoted, ramp actuated, pusher arm for effecting final discharge of the trolleys where the tracks pass through a switch point. The same ramping system may be used to effect a positive propelling member to trolley lock of one or both arms where the system incorporates a vertical incline. The ramps may be retractably mounted to provide selectivity in operation.

United States Patent 1 Price et al. I

7 [111 3,744,432 [4 1 July 10,1973

1 1 TROLLEY DIVERTER [75] Inventors; Peter P. Price, Cascade; Nathan C.

Snyder, Grand Rapids, both of Mich.

[73] Assignee: Rapistan Incorporated, Grand Primary Examiner-'Drayton E. Hoffman Attorney-Price, l-leneveld, Huizenga & Cooper [57] f, aBSTRACT The system has over and under propelling member and trolley tracks of constant spacing. The propelling member has a depending driving arm for engaging the trolleys and a normally retracted pivoted, ramp actuated, pusher arm for effecting final discharge ofv the trolleys where the tracks pass through a switch point. The same ramping system-may be used to effect a positive propelling member to trolley lock of one or both arms where the system incorpora tes a vertical incline. The ramps may be retractably mounted to provide selectivity in operation.

'10 Claims, 16 Drawing Figures PATENTED 3. 744.432 I SHEH 1 0F 6 BY ww mvsmons PATEMEW W I 3.744.432

SHEU 2 BF 6 INVENTORS M4 77/441 a l ra e PATENTEDJUUUW 3.744.432

INVENTORS A/ATZ/AA/ a. saw nae PATENTED JUL 1 0 3. 744.432

PATENIEU 1 3. 744.432

- 6? END /V 45 a C: 10 I id //VCL//VV TRACK FIG. I5.

INVENTOR? AMT/mu a. .swmae TROLLEY DIVERTER FIELD OF INVENTION This invention relates to improvements in conveyors of the power and free type in which carriers are propelled along a load supporting track by either puller arm or a pusher arm mounted on an endless propelling member supported on a parallel track for engaging drive dogs on the carriers. More specifically, the invention, in one phase, pertains to improved means for transferring the carriers from one track to another and related interlock means for moving the carriers when travelling an inclined portion of the track.

DESCRIPTION OF THE PRIOR ART Over and under, power and free conveyors designed to provide transfer of the trolleys between a main or primary track and a spur or secondary track are wellknown in the art. Existing patents disclose various means of moving the trolleys across the power interruption or gap which exists at the switch point where th two tracks merge. One of the more commonly used arrangements is shown in U.S. Pat. No. 3,314,377 entitled CONSTRUCTION FOR TRANSFERRING A CONVEYOR CARRIER BETWEEN POWER LINES, issued to CA. Dehne Apr. 18, 1967. This arrangement uses a pair of depending pushers on the propelling member with the lead pusher longer than the trailing pusher. The trailing pusher is too short to engage the trolleys when the power and trolley tracks are at norma] spacing. The vertical spacing between the tracks is reduced at the switch points, permitting the trailing pusher to engage the trailing trolley and push the carrier either off or onto th main track. The same result is accomplished when the pushers on the propelling member are of identical length but the dogs on the trolley are of different lengths as disclosed in US. Pat. No. 3,229,645 entitled POWER AND FREE CONVEY- ORS, issued to CA. Dehne Jan. 18, 1966. Reducing the spacing between the power and load tracks is also used to effect a positive lock between the propelling member and the trolleys where the track is inclined. This is disclosed in US. Pat. No. 2,510,318 entitled VERTICAL CURVE SECTION FOR POWER- DRIVEN AND FREEWHEELING TROLLEY CON- VEYORS, issued to A.G. Rose on June 6, 1950. The

provision of means on conveyors of this type to permit accumulation of carriers is also known.

SUMMARY OF. INVENTION variation in track spacing." These objectives are accomplished while retaining the conveyors ability to accumulate carriers when desired.

The objects of this invention are accomplished'by providing a single, pivoted driving dog or arm having integral drive and holdback means which cooperate Cooperating with the driving arm is supplementary or pusher arm mounted on the propellingmember. Th

pusher arm is spaced rearwardly from the driving arm a length greater than that of a carrier. The pusher arm is pivoted to the propelling member at its rear end and is biased into normally retracted position generally parallel to th propelling member. It is equipped with a laterally projecting pin adjacent its free end. This pin is on the opposite side of the conveyor from the pin on the drivingarm. At those sections of the conveyor where the pusher arm is needed, such as at a switch point, a

; rampis provided on the power track. Engagement of the ramp by the pin forces the pusher arm to extend downwardly where it engages an upwardly extending some bends In the power track which are necessary with a driving dog and release post on the foward trolley of a carrier. The driving arm has a laterallypr ojecting pin on one side which cooperates with a rampon the power track to effect a positive lock along in- 'clined portions of the conveyor.

when the spacing between the tracks is varied. The invention permits much greater flexibility in conveyor design and makes modification of the conveyor comparatively simple, when changing requirements necessitate such changes. It also permits a greater degree of standardization to be introduced into the conveyor eliminating much of the custom engineering of each in-. stallation which has characterizedthe design of these conveyors using existing constructions.

Other features and advantages of the invention-will appear from the description to follow the embodiments disclosed in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view showing the power and load tracks and a carrier together with the means of propelling it according to this invention;

FIG. 2 is a vertical section taken along line II-II of FIG. 10;

FIG. 3 is an enlarged exploded, perspective viewof the pusher arm;

FIG. 4 is a fragmentary sectional view of the pusher arm only taken along the plane IV--IV of FIG. 2;

FIG. 5 is a fragmentary perspective view of the forward trolley of a carrier with the drawing arm ramped into locked engagement such as would occur along a section of inclined track;

FIG. 6 is a fragmentary, partially broken plane view taken through the load track at a switch point;

FIG. 7 is a fragmentary plan view of a typical switch point showing both the power and load tracks;

FIGS. 8, 9 and 10 are fragmentary side elevational views showing progressively the interaction of the driving and pusher arms and a trolley at a switch point;

FIG. 11 is a fragmentary sectional elevation view of a trolley stop foreffecting accumulation:

FIGS. 12, 13 and 14 are fragmentary side elevational views showing progressively the interaction of the driving arm and trolleys during accumulation;

FIG. 15 is a schematic representation of a conveyor showing the locations at which actuator ramps are used in accordance with this invention; and

FIG, 16 shows a modified ramp construction with the ramps in operative position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring specifically to FIG. 1, the conveyor is of the well-known over and under, power and free type. The conveyor is propelled by a driven chain 11 which travels in and is supported by the closed power track 12. Vertically spaced beneath the power track 12 is the trolley track 13 which also is of conventional closed construction. The tracks 12 and 13 are rigidly joined together at suitable intervals throughout the system by any of the several well-known structures long used in this field.

Each load carrier 14 is supported from the trolley track 13 by a pair of spaced trolleys, a front or lead trolley 15 and a rear or trailing trolley 16. The trolleys 15 and 16 are connected by rigid load bar 17. The connection between the load bar and each of the trolleys incorporates a pivot 19 (FIG. 1). Each trolley travels on wheels 18. All of the preceding described structure is conventional and well-known to the conveyor art and further detailed description is not considered necessary to an understanding of the invention.

The forward or lead trolley 15 has an upstanding post 30. The post 30 is a primary drive post and has a downwardly flared base 31 and an inverted frusto-conical top 32' giving a somewhat hourglass shape to the post 30. Spaced rearwardly from the post 30 is a forward drive release member 33 having an elongated top 35 and a rearwardly dependingli p 34 serving as a ramp.

The rear or trailing trolley has a rear drive release member 36 of the same construction as the forward releasr member 33. It also has an elongated top 38 and a rearwardly depending lip 37. Under certain operating conditions, the rear drive release member serves as a secondary drive post as will become clear in the following description. The top of the post 30 and the tops 35 and 38of the forward and rear drive release members are in the same general plane. The rear drive release member 36 is located at the rear end of the trailing trolley 16 and a portion of it extends rearwardly beyond the end of the trolley.

Rigidly mounted to the chain 11 is forward bar 40.

The bar 40 depends from the chain ll b elow the power track 12. Beneath the bar 40 is a drive dog 41. Its forward end is pivotally mounted at 42 to the forward end of the bar 40. The rearward or trailing end of the drive dog is urged downwardly by gravity and incorporates a socket 43, the downwardly opening end of which is partially restricted as best seen in FIGS. 12 and 13. The width of the socket entrance is sufficient to permit the top 32 of the p6st 30 to enter the socket and the partial restriction of the entrance creates a socket configuration generally conforming to the configuration of the post top 32. Both forwardly and rearwardly of the socket entrance the lower face of the drive dog is inclined upwardly creating both a forward ramp 44 and a rearward ramp 45. Projecting laterally from the drive dog, adjacent its free or trailing end, is a pin 46.

Also mounted on the chain is an auxiliary drive 50. The auxiliary drive 50 is spaced rearwardly from the drive dog 41 a distancegreater than the spacing between the post 30 and the trailing drive release 36. The auxiliary drive 50 has a .drive arm 51 the rear end of which is pivotally mounted at 52 to the plate 53 which, in turn, is mounted to the chain 11. The forward end of the drive arm 51 is free and the arm is urged upwardly into retracted position (as illustrated in FIG. 1) by a spring 54 (FIG. 4). Its downward pivotal movement is limited by a stop 55.

The forward or free end of the am 51 has a laterally projecting pin 56. The pin'56 projects from the side of the arm opposite to that of the pin 46 on the drive dog 41. The purpose of this will appear more fully hereinaftrated in FIG. 15. Such conveyors normally incorporate one ormore secondary or spur tracks 61. Such secondary tracks may be used for trolley accumulation or'as a diversion through a secondary processing area or for any other reason. Frequently, it is necessary that the track change elevatuon, necessitating inclination of and 62a in FIG. 15. This invention is particularly concerned with the propelling of the trolleys at the switches 63 where the secondary and primary tracks come together and the inclined portions of the track.

It has long been conventional both at the switch areas 63 a a r cl ns l lttims. 6.2 tt ist a i9 .rq ss the spacing between the power track 12 and the trolley track 13 by offsetting thepower track downwardly toward the chain track. In switch areas; this permits a trailing auxiliary drive of fixed vertical projection to be moved into position to engage the rear end of a trolley after the front end has been diverted onto a spur track and disengaged by the forward or primary drive. The auxiliary drive the completes the diversion of thetrolley by pushing it off the main track. After passing the switch area, the track spacing is returned to normal, rendering the auxiliary drive inoperative. In this arrangement, the spacing of the tracks is the sole means by which the op erativeness of the auxiliary time is controlled. 7

In areas where the track is inclined, the track spacing is also reduced to positively lock the primary drive against inadvertent disengagement from the trolley due to the additional load imposed upon it.

The variation in track spacing for these purposes works but is unsatisfactory for several reasons.

Fabrication of the bends 'in the power track is costly and substantially increases the overall cost of the unit. Further, the bends create points of added wear and resistance to chain movement, therefore, increasing the conveyors overall power demand and operating costs. It also makes modification of an existing conveyor to add or delete switches a costly, expensive and time consuming operation.

' The S am tracks 5593s sawrd'ai unpowered: If they are powered, they are equipped with a power track similar to that of the main conveyor, having a separate drive chain and, like the chain of the main conveyor, equipped with a forward drive dogand an I auxiliary drive. Movement of the drive chain of the spur track is synchronized to that of the chain of the main conveyor, normally through a slave drive arrangement. In the case of unpowered spurs, the trolley track is frequently slightly inclined adjacent the main track to bias the load carriers either away from i v or toward the main track, depending'upon whether they are designed to receive load carriers from or to discharge them onto the main track. In the following description, it will be assumed that the spur track is powered.

In the present-invention, a typical switch 63 is illustrated in FIGS. 6 and 7. FIG. 6 illustrates only the trolley track with the top partially cutaway. Diversion of the trolley is effected by. the switch tongue 70. With a load carrier moving in the direction of the arrow A and the tongue 70 shifted to the position The auxiliary drive 50 now takes over and completes I the shunting of the load carrier onto the spur track. Since the-drive arm 510i the auxiliary drive is normally retracted and inoperative, it must be shifted tooperative position to do this. This is accomplished by a ramp 80 mounted on the power track 12 (See FIGS. 8, 9 and 10). The ramp 80 is mounted on the side on the side of the power track to intercept the pin 56 on the drive arm 5?. Asthe chain in the power track moves the load car rier' 14 in the direction of the arrow B, FIG. 9 illustrates the lowering of the drive arm 51 by engagement between the ramp 80 and the pin 56. The length of the ramp 80 is such that this occurs sometime just prior to or simultaneously with the disengagement of the drivedog 41 from the'post 30 due to the lateral movement of the lead trolley 15. Because of the spacing between drive dog 41 and the auxiliary arm 50, there is a short lapse during which the load carrier remains stationary. However, as soon as the drive arm 51 engages the rear end of the trailing release member 36, movement of the load carrier will be reinitiated and will continue until the rear trolley has been pushed off the main track. During this operation, the rear or trailing release member functions as an auxiliary drive post. After this has occurred, the ramp 80 will cease, permitting the drive arm 51 to retract. It will be noted that the pin on the drive dog 41. since it projects oppositely from the pin on the drive arm, is not affected by the ramp 80.

As is shown in FIG. 7, closely adjacent the switch 63, the power track 61b and its drive chain bend into load carrier drive position over the trolley track 61a of the spur track. The forward trolley of a diverted load carrier after it has been pushed off the main track by the auxiliary drive, is positioned, such that the next approaching drive dog on the chain on the power track 6lb will engage the drive post 30 of the load carrier and pull it along the spur track. If the spur track is nonpowered, the effect of the auxiliary drive of the main track is to push the load carrier to a position where gravity will cause the load carrier to move away from the main track, at least sufficiently to clear the switch area.

Where the switch is one at which load carriers enter the main track from the spur track, the procedure is reversed. Here the drive dog of the spur track will release the load carrier just before it reaches the switch because the drive dog will shift laterally with respect to the load carrier. Here a ramp 80 is provided on the spur track to activate the following auxiliary drive on the spur track chain. The auxiliary drive will push the load carrier, moving its forward trolley onto the main track where its post 30 will be captured by the next passing drive dog on.the drive chain of the main conveyor.

I have long been used in this type of conveyor and are,

therefore, not illustrated or described here.

When the track is inclined another ramp 81,-

mounted on the opposite side of the power track is used (FIG. 5). The ramp 81 engages the pin 46 on the drive dog 41 locking it down in engagement with the post 30. This prevents inadvertent pivoting of the drive dog to release the post due to heavy loads. Again, the use of a ramp eliminates the necessity for varying track spacing. If additional security is desired at inclined sections, both ramps 81 and 80 may be provided. This will lower the drive arm 51 to block the rearward movement of a load carrier should it, for any reason, become released from the drive dog while ascending an incline.

There may be situations in which it is desired to selectively activate the drive arm 51 for certain load carriers but not others. This can be done by providing a retractable ramp. One arrangement for doing this illustrated in FIG. 16. Here theramp 80a is, mounted on a support 85 pivoted at 86. The arm is moved by suitable means such as the solenoid 87 to shift the ramp 80 from operating position (shown in solid lines) to retracted or inoperative position (shown in phantom). It will be recognized that various other arrangements for rendering the ramp selectively operative are within the skill of the art.

This invention permits accumulation. When accumulation is to occur, a positive stop, 90 is provided to prevent further movement of the lead trolley. Such a stop is illustrated in FIG. 11. In this construction, a stop plate 91 is mounted to be shifted between active and retracted positions by any suitable means such as the solenoid 92. The stop plate 91 is so located that is upper surface is flush with the top of the release members 33 and 36. As a load carrier, being pulled by the drive dog 41, approaches the extended stop plate 91, engagement of the forward ramp 44 of the drive dog with the stop plate 91 lifts the drive dog sufficiently to disengage the post 30 of the forward trolley. This reretracted or drive post release position and holds the drive dog in retracted position until it has cleared the rear drive release. When the following, drive dog 41 approaches it will be pivoted to retracted position by the forward drive release 33. Because of the spacing between the post 30 and the rear drive release 36 of the lead until it has cleared the rear drive release of the lead trolley and thus passes over the post 30 without shifting into post capturing position.

To release the accumulated load carrier from accumulation, it is only necessary to retract the stop plate 91. The next approaching drive dog will then drop on and engage the post 30 of th lead load carrier and its forward movement will be restored. This will automatically permit the next following drive dog to engage the next load carrier and remove it. This sequence will be repeated until all of the accumulated load carriers are once more in motion. Because the drive arm 51 of the auxiliary drive is always retracted to inoperative position unless a ramp is provided, it does not, in any way, interfere with the accumulation function. The arrangement provides a extremely simple, positive and dependable accumulation capability.

It will be seen that this invention provides a simple and dependable solution to the problem of providing load carrier switching and accumulation in the same conveyor and at the same time equipping the conveyor with a safety lock on inclines. it also markedly simplifies the job of modifying the conveyor, especially at track junction.

While a prefered embodiment has been illustrated and described, it will be recognized that various modifications of the invention can be made embodying the principlesv herein disclosed. Such modifications are to be. considered to be within the hereinafter appended claims unless the language of the claims specifically states to the contrary.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A power and free conveyor having spaced trolley and power tracks and a driven propelling member mounted in said power track, at least one elongated load carrier supported on said trolley track for travel therealong, said load carrier having a primary drive post at its leading end and an auxiliary drive post at its trailing end, a primary drive on said propelling member adapted to engage said primary drive post, an auxiliary drive on said propelling member spaced from said primary drive a distance greater than the spacing between said primary'and secondary drive posts, the improvement in said conveyor comprising: maintaining a constant spacing between said power and trolley tracks throughout said conveyor; said primary drive having a drive arm movable between an extended primary drive post engaging position and a retracted postion disengaged from said primary drive post, said drive arm being urged by its own weight into said extended position; said auxiliary drive having a pusher arm pivotally mounted thereon and means biasing said pusher arm into retracted position disengaged from both said primary and secondary drive posts; actuating means at selected positons along said conveyor for engaging said pusher arm, urging said pusher arm into extended position and holding said pusher arm in said extended position; said pusher arm, when so extended, being engageable with said auxiliary drive post for transmitting motion from said propelling member to said load carrier.

2. A conveyor as described in claim 1 wherein said actuating means is movably mounted on said power track; said conveyor including an actuator for shifting said actuating means from a first position whereat it engages said pusher arm to a second position whereat it will not engage said pusher arm.

3. A conveyor as described in claim 2 wherein said actuating means is an elongated ramp mounted on said power track, said pusher arm including follower means engageable with said ramp for actuating said pusher arm.

4. A conveyor as described in claim 1 wherein a second actuating means is provided at selected positions for locking said drive arm in said extended position.

5. A conveyor as described in claim 4 wherein said second actuating means is inefi'ective to actuate said pusher arm and said first actuating means is ineffective to actuate said drive arm.

6. A conveyor as described in claim 4 wherein one or more of said selected positions for said second actuating meansis along conveyor sections of vertical incline.

7. A power and free conveyor having spaced trolley and power tracks and a driven propelling member mounted in said power track, at least one elongated load carrier supported on said trolley track for travel therealong, said load carrier having a primary drive post at its leading end and an auxiliary drive post on its trailing end, a primary drive dog on said propelling member adapted to engage said primary drive post, an auxiliary drive on said propelling member spaced from said primary drive dog a distance greater than the spacing between said primary and secondary drive posts, the improvement in said conveyor comprising: vmaintaining a constant spacing between said power and trolley tracks throughout said conveyor; said primary drive dog having coupling means for drivingly engaging said primary drive post; said auxiliary drivepost being so shaped as to be incompatible and non-drivingly engageable with said coupling means; when a following load carrier abuts the load carrier aheadof it, said auxiliary drive post of said leading load carrier being immediately adjacent the primary drive post of the following load carrier and supporting said primary drive dog into non-coupling position with. respect to said primary drive post; said auxiliary drive having a drive arm pivotally mounted thereon and means pivotally mounted thereon and means biasing said dribe arm into retracted position disengaged from both said primary and secondary drive posts; actuating means at selected positions along said conveyor for engaging said drive arm, urging said drive arm into extended position and holding said drive arm in said extended position; said drive arm, when so extended, being engagable with saidauxiliary drive post for transmitting motion from saidpropelling member to said load carrier.

8. A power and free conveyor having spaced trolley and power tracks and a driven propelling member mounted in said power track, at least one elongated load carrier supported on said trolley track for travel therealong, said load carrier having interconnected lead and trailing trolleys; said load carrier having a primary drive post at the forward end of its lead trolley and an auxiliary drive post at the rear end of its trailing trolley; a primary drive dog pivotally mounted at its forward end to said propelling member, the rearward end of said primary drive being free and biased downwardly; said primary drive dog adjacent its free end having a coupling socket, a first cam surface extending forwardly from and a second cam surface extending rearwardly from said coupling socket, said coupling socket opening downwardly and having a restricted entrance in a fore and aft direction, an auxiliary drive on said propelling member spaced from said primary drive dog a distance greater than the spacing between said primary and secondary drive posts, the improvement in said conveyor comprising: maintaining a constant spacing between said power and trolley tracks throughout said conveyor; the tops of said primary and auxiliary drive posts being substantially in the same plane parallel to said trolley track and projecting into the path of travel of the free end of said primary drive dog; the top of said auxiliary drive post being non-complimentary with said coupling socket whereby saidprimary drive dog will not couple therewith; said auxiliary drive having a drive arm pivotally mounted thereon and means biasing said drive arm into retracted position disengaged from both said primary and secondary drive posts; actuating means at selected positions along said conveyor for engaging said drive arm, urging said drive arm into extended position and holding said drive arm in said extended position; said drive arm, when so extended, being in the path of and engageable with said auxiliary drive post for transmitting motion from said propelling member to said load carrier.

9. A power and free conveyor as described in claim 8 wherein when two of said load carriers are in substantially abutting relationship the auxiliary drive post of 10 the forward one of said load carriers is immediately adjacent the primary drive post of the rearward one of said load carriers, said auxiliary drive post engaging said forward cam surface of said primary drive dog to pivot it out of engagement with the primary drive post of the rearward of said load carriers.

10. A power and free conveyor as described in claim 9 wherein a release post, similar to said auxiliary drive post is mounted on the forward one of said trolleys of each load carrier and spaced rearwardly thereof a distance greater than the spacing between said coupling ward one of said load carriers.

. UNIT ED S C I ATES LP ZATENT OFFICE CORRECTION a r 3 744 432 n v Dated July 10, 1973 v i l-atent No. v

IUVEIltO'LiS) Pet e i P. Price And Nathan C. Snyder I i; is; certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 34!;

"th" should read the Column ,2 line.

"Th" should he The Column 3, line 30 "dependingli vp" should be depending lip Column 4', 11m Zlr "e1evatuon" should be elevation Column 6, line 46:

"that 1 should be that its Column 6, line 66:

After 'flead"insert therefor load carrier,

the drive dog 41 will be retained in retracted position Column 8 39 v "dribe" should be we drive Signed and eealed this 20th day or November 1973.

(SEAL) Attest:

EDWARD -M.FIETCHER,JR.' RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

1. A power and free conveyor having spaced trolley and power tracks and a driven propelling member mounted in said power track, at least one elongated load carrier supported on said trolley track for travel therealong, said load carrier having a primary drive post at its leading end and an auxiliary drive post at its trailing end, a primary drive on said propelling member adapted to engage said primary drive post, an auxiliary drive on said propelling member spaced from said primary drive a distance greater than the spacing between said primary and secondary drive posts, the improvement in said conveyor comprising: maintaining a constant spacing between said power and trolley tracks throughout said conveyor; said primary drive having a drive arm movable between an extended primary drive post engaging position and a retracted postion disengaged from said primary drive post, said drive arm being urged by its own weight into said extended position; said auxiliary drive having a pusher arm pivotally mounted thereon and means biasing said pusher arm into retracted position disengaged from both said primary and secondary drive posts; actuating means at selected positons along said conveyor for engaging said pusher arm, urging said pusher Rm into extended position and holding said pusher arm in said extended position; said pusher arm, when so extended, being engageable with said auxiliary drive post for transmitting motion from said propelling member to said load carrier.
 2. A conveyor as described in claim 1 wherein said actuating means is movably mounted on said power track; said conveyor including an actuator for shifting said actuating means from a first position whereat it engages said pusher arm to a second position whereat it will not engage said pusher arm.
 3. A conveyor as described in claim 2 wherein said actuating means is an elongated ramp mounted on said power track, said pusher arm including follower means engageable with said ramp for actuating said pusher arm.
 4. A conveyor as described in claim 1 wherein a second actuating means is provided at selected positions for locking said drive arm in said extended position.
 5. A conveyor as described in claim 4 wherein said second actuating means is ineffective to actuate said pusher arm and said first actuating means is ineffective to actuate said drive arm.
 6. A conveyor as described in claim 4 wherein one or more of said selected positions for said second actuating means is along conveyor sections of vertical incline.
 7. A power and free conveyor having spaced trolley and power tracks and a driven propelling member mounted in said power track, at least one elongated load carrier supported on said trolley track for travel therealong, said load carrier having a primary drive post at its leading end and an auxiliary drive post on its trailing end, a primary drive dog on said propelling member adapted to engage said primary drive post, an auxiliary drive on said propelling member spaced from said primary drive dog a distance greater than the spacing between said primary and secondary drive posts, the improvement in said conveyor comprising: maintaining a constant spacing between said power and trolley tracks throughout said conveyor; said primary drive dog having coupling means for drivingly engaging said primary drive post; said auxiliary drive post being so shaped as to be incompatible and non-drivingly engageable with said coupling means; when a following load carrier abuts th load carrier ahead of it, said auxiliary drive post of said leading load carrier being immediately adjacen the primary drive post of the following load carrier and supporting said primary drive dog into non-coupling position with respect to said primary drive post; said auxiliary drive having a drive arm pivotally mounted thereon and means pivotally mounted thereon and means biasing said dribe arm into retracted position disengaged from both said primary and secondary drive posts; actuating means at selected positions along said conveyor for engaging said drive arm, urging said drive arm into extended position and holding said drive arm in said extended position; said drive arm, when so extended, being engagable with said auxiliary drive post for transmitting motion from said propelling member to said load carrier.
 8. A power and free conveyor having spaced trolley and power tracks and a driven propelling member mounted in said power track, at least one elongated load carrier supported on said trolley track for travel therealong, said load carrier having interconnected lead and trailing trolleys; said load carrier having a primary drive post at the forward end of its lead trolley and an auxiliary drive post at the rear end of its trailing trolley; a primary drive dog pivotally mounted at its forward end to said propelling member, the rearward end of said primary drive being free and biased downwardly; said primary drive dog adjacent its free end having a coupling socket, a first cam surface extending forwardly from and a second cam surface extending rearwardly from said coupling socket, said coupling socket opening downwardly and having a restricted entrance in a fore and aft direction, an auxiliary drive on said propelling member spaced from said pRimary drive dog a distance greater than the spacing between said primary and secondary drive posts, the improvement in said conveyor comprising: maintaining a constant spacing between said power and trolley tracks throughout said conveyor; the tops of said primary and auxiliary drive posts being substantially in the same plane parallel to said trolley track and projectinginto the path of travel of the free end of said primary drive dog; the top of said auxiliary drive post beng non-complimentary with said coupling socket whereby said primary drive dog will not couple therewith; said auxiliary drive having a drive arm pivotally mounted thereon and means biasing said drive arm into retracted position disengaged from both said primary and secondary drive posts; actuating means at selected positions along said conveyor for engaging said drive arm, urging said drive arm into extended position and holding said drive arm in said extended position; said drive arm, when so extended, being in the path of and engageable with said auxiliary drive post for transmitting motion from said propelling member to said load carrier.
 9. A power and free conveyor as described in claim 8 wherein when two of said load carriers are in substantially abutting relationship the auxiliary drive post of the forward one of said load carriers is immediately adjacent the primary drive post of the rearward one of said load carriers, said auxiliary drive post engaging said forward cam surface of said primary drive dog to pivot it out of engagement with the primary drive post of the rearward of said load carriers.
 10. A power and free conveyor as described in claim 9 wherein a release post, similar to said auxiliary drive post is mounted on the forward one of said trolleys of each load carrier and spaced rearwardly thereof a distance greater than the spacing between said coupling socket and the rearward end of said primary drive dog, and when said load carriers are in substantially abutting relationship the tops of said auxiliary drive post of the forward load carrier and said release post cooperating to hold said drive dog pivoted into disengaged position as it is moved over the primary drive post of the rearward one of said load carriers. 